Fan Fiction a good way to write without worrying about First Rights

All right, you may think, well only teenagers write fan fiction. Once you get to be a woman of a certain age, forget about it. You are too old and dignified unless you are writing a Murder She Wrote fan fiction. Well I love to write fan fiction, I would love to write a story about NCIS, but have no idea whether Tony will fall in love, since I did write one about Law and Order: Criminal Intent and they did not follow my romantic inclinations, so I stick with shows that have been canceled or have not been around for some time.
I find in Fan fiction (I love crossovers) that if there are villains or space aliens, the Homo Dominants in Prey, that people love to even the playing field. Great, I watch a show and I see the people have no chance against these shape shifting aliens, so why suddenly make the aliens not being able to stand sunlight or all you have to do is to push them outside? Another thing I notice, that if in the story, the girl or boy who was raised by evil people, and then later on reforms and turns out to be nice, the reason was not that he or she came to his or her senses or someone convinced her that shooting everybody was wrong, but that she is really not the daughter of that evil person, but in reality the daughter of the handsome prince or the good doctor.
Now how do you make Crossovers? You have a connection. In some cases as in a future episode, the CSI team or rather Grissom has to go to New York to cooperate with the Without a Trace Team and even if it is not shown, or the show was canceled, you can use parts of each show to make the Crossover natural. For instance, I connected The Pretender with Prey, with two episode, Jarod jumping off a boat and swimming to shore, and jumping off a building onto Broot's car. Normally he would have died from that distance. In the same way, you can connect, since House is in Boston and since Boston Law is in Boston, if there is an episode where a lawyer has a sudden attack and taken to the hospital.
Now the good thing about Fan Fiction is that you can show your talent and practice on it. You do not have to worry that you are losing your first rights, unless you are given a contract to write a Star Trek or a Buffy, etc. story. You do have to tell everyone that the characters, other than the ones you made up, belong to the owners, the original writers, and to what station they gave them to, but that is all.
So get writing about your favorite Movie or TV characters in those spare moments and when you are not working on your novel and or short story.